The present invention relates to an improved catalyst based on cobalt and/or rhodium used in a two-phase medium. The catalyst based on cobalt and/or rhodium, which comprises at least one cobalt and/or rhodium complex co-ordinated with at least one nitrogen-containing ligand, is dissolved in a non-aqueous ionic solvent which is liquid at a temperature of less than 90xc2x0 C., in which the aldehydes formed are slightly soluble or insoluble. The catalyst is particularly useful for the hydroformylation of olefinically unsaturated compounds.
Hydroformylation of olefinic compounds is a reaction of major industrial importance and the majority of processes use homogeneous catalysts dissolved in an organic phase constituted by the reactants, products and possibly excess ligand, although difficulties are encountered in separating and recovering the catalyst, in particular when it is used in relatively large quantities, as is the case with catalysts based on cobalt or on a noble metal, as is the case with rhodium-based catalysts.
One solution aimed at solving that problem has been developed by Bartik et al., Organometallics (1993), 12, 164-170, J. Organometal. Chem. (1994), 480, 15-21, and by Beller et al., J. molecular Catal. A: Chemical (1999), 143, 31-39. It consists of carrying out hydroformylation in the presence of an aqueous solution containing a cobalt complex which is rendered water-soluble by the presence of a phosphine-sulfonate ligand such as the sodium salt of trisulfonated triphenylphosphine or a trisulfonated tris-(alkylphenyl)phosphine. International Patent Application WO 97/00132 describes cobalt clusters substituted by trialkoxysilylmethyl groups which render them water-soluble. In that manner, the organic phase containing the aldehydes is readily separated from the aqueous phase containing the catalyst.
A further solution aimed at solving that problem has been described in French Patent No. 2 314 910. It consists of carrying out hydroformylation in the presence of an aqueous solution containing a rhodium complex which is rendered water-soluble by the presence of a sulfonated phosphine ligand which is itself water-soluble, such as the sodium salt of trisulfonated triphenylphosphine. In that manner, the organic phase containing the aldehydes is readily separated from the aqueous phase containing the catalyst. That technique has been studied widely and those studies have been discussed in an article by W. A. Herrmann in xe2x80x9cAngewandte Chemie Internationalxe2x80x9d, 1993, volume 32, pages 1524 ff.
Despite the huge industrial importance of such techniques for hydroformylation of propylene, such two-phase systems suffer from a lack of solubility of olefins in water, leading to relatively low reaction rates, which render them unsuitable for long chain olefins.
U.S. Pat. No. 3,565,823 describes a technique consisting of dispersing a transition metal compound in a quaternary ammonium or phosphonium salt of tin or germanium with formula (R1R2R3R4Z)YX3 where R1, R2, R3, and R4 are hydrocarbyl residues containing up to 18 carbon atoms, Z is nitrogen or phosphorous, Y is tin or germanium and X is a halogen, for example chlorine or bromine.
U.S. Pat. No. 3,832,391 claims a process for olefin carbonylation using the same composition. The above compositions have the disadvantage of having a relatively high melting point, for example over 90xc2x0 C., which complicates manipulation of the catalyst solutions and the reaction products.
U.S. Pat. No. 5,874,638 describes that it is possible to benefit both from the advantages of a two-phase operation while avoiding the disadvantages linked to using water and to
using compounds with a high melting point, by dissolving certain catalytic compounds of transition metals from groups 8, 9 and 10, known to catalyze hydroformylation, in non-aqueous ionic solvents which are constituted by organic-inorganic salts which are liquid at ambient temperature.
It has now been discovered that the activity and selectivity for the hydroformylation reaction of catalysts based on cobalt and/or rhodium used in an ionic non-aqueous solvent which is liquid at a temperature of less than 90xc2x0 C. are greatly improved by using nitrogen-containing ligand to complex the cobalt and/or rhodium. The present invention focuses on the novel catalyst system.
More precisely, the invention provides a catalyst composition comprising at least
one complex of cobalt and/or rhodium co-ordinated by at least one nitrogen-containing ligand, and of at least one non-aqueous ionic solvent comprising at least one organic-inorganic salt with general formula Q+Axe2x88x92, where Q+ represents a quaternary ammonium and/or quaternary phosphonium cation and Axe2x88x92 represents an anion, with the provision that the at least one ligand is devoid of tertiary phosphines, stibnines, arsines and phosphates.
The cobalt and/or rhodium precursor compounds of the catalyst are selected from the group formed by cobalt and/or rhodium salts such as acetylacetonates, carboxylates, in particular formate or acetate, and carbonyl complexes, such as dicobalt-octacarbonyl, cobalt-tetracarbonyl hydride, rhodium-dicarbonyl acetylacetonate and carbonyl clusters. The choice of the cobalt and/or rhodium precursor compound is not critical, but in general it is preferable to avoid halides.
The nitrogen-containing ligand is preferably selected from the group formed by monoamines, di-, tri- and polyamines, imines, diimines, pyridine and substituted pyridines, bipyridine, imidazole and substituted imidazoles, pyrrole and substituted pyrroles, pyrazole and substituted pyrazoles. Non limiting examples which can be cited are triethylamine, ethylene diamine, tetramethyl-ethylenediamine, diethylenetriamine, diazabicyclooctane, 1,4,7-trimethyl-1,4,7-triazacyclononane, N,Nxe2x80x2-dimethyl-ethane-1,2-diimine, N,Nxe2x80x2-di-tert-butyl-ethane-1,2-diimine, N,Nxe2x80x2-di-t-butyl-butane-2,3-diimine, N,Nxe2x80x2-diphenyl-ethane-1,2-diimine, N,Nxe2x80x2-bis-(2,6-dimethylphenyl)-ethane-1,2-diimine, N,Nxe2x80x2-bis-(2,6-diisopropyl-phenyl)-ethane-1,2-diimine, N,Nxe2x80x2-bis-(2,6-di-t-butyl-phenyl)-ethane-1,2-diimine, N,Nxe2x80x2-diphenyl-butane-2,3-diimine, N,Nxe2x80x2-bis-(2,6-dimethyl-phenyl)-butane-2,3-diimine, N,Nxe2x80x2-bis-(2,6-diisopropyl-phenyl)-butane-2,3-diimine, N,Nxe2x80x2-bis-(di-t-butyl-2,6-phenyl)-butane-2,3-diimine, pyridine, picolines, t-butylpyridine, bipyridine, di-t-butyl-bipyridine, imidazole, N-methylimidazole, N-butylimidazole, benzimidazole, pyrrole, N-methylpyrrole and 2,6-dimethylpyrrole.
The nitrogen-containing ligand can also include other organic functions, such as alcohol, aldehyde, ketone, carboxylic acid, ester, nitrile, quaternary ammonium and/or phosphonium, also sulfonium functions. Non limiting examples which can be cited are picolinic acids and esters, 2,6-dialkoxypyridines, salicylaldimines, 2,6-bis-N-aryliminopyridines, 1-dialkyl (and diaryl) phosphino-2-(4-pyridyl)ethanes, alkyl 2-(4-pyridyl)-acetates, alkyl 2-(2-pyridyl)-acetates, ethylene glycol bis-3-(4-pyridyl)-propanoate, 2-(2-pyridyl)-ethanol, 3-(2-pyridyl)-propanol and 3-(2-pyridyl)-propyl acetate.
The non-aqueous ionic solvent is selected from the group formed by liquid salts with general formula Q+Axe2x88x92 where Q+ represents quaternary ammonium and/or quaternary phosphonium and Axe2x88x92 represents any anion which can form a liquid salt at low temperature, i.e., below 90xc2x0 C. and advantageously at most 85xc2x0 C., preferably below 50xc2x0 C. Preferred anions Axe2x88x92 are acetate, halogenoacetate, tetrafluoroborate, tetrachloroborate, hexafluorophosphate, hexafluoroantimonate, fluorosulfonate, perfluoroalkylsulfonate, bis-(perfluoroalkylsulfonyl)amide and arene-sulfonate ions.
The quaternary ammonium and/or phosphonium ions preferably have general formula NR1R2R3R4+ and PR1R2R3R4+ or general formula R1R2Nxe2x95x90CR3R4+ or R1R2Pxe2x95x90CR3R4+, where R1,R2, R3, and R4, which may be identical or different, represent hydrogen (with the exception of the NH4+ cation for NR1R2R3R4+), preferably a single substituent representing hydrogen, or hydrocarbyl residues containing 1 to 12 carbon atoms, for example saturated or unsaturated alkyl, cycloalkyl or aromatic generals, aryl or aralkyl groups containing 1 to 12 carbon atoms. The ammonium and/or phosphonium can also be a derivative of nitrogen-containing and/or phosphorus-containing heterocycles containing 1, 2 or 3 nitrogen and/or phosphorus atoms, in which the cycles are constituted by 4 to 10 atoms, preferably 5 to 6 atoms.
The quaternary ammonium and/or phosphonium can also be a cation with formula:
R1R2+Nxe2x95x90CR3xe2x80x94R5xe2x80x94R3Cxe2x95x90N+R1R2 
and/or
R1R2+Pxe2x95x90CR3xe2x80x94R5xe2x80x94R3Cxe2x95x90P+R1R2 
where R1, R2 and R3, which may be identical or different, are defined as above, and R5 represents an alkylene or phenylene residue. Examples of groups R1, R2, R3, and R4 which can be mentioned include the following radicals: methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, tertiary butyl, amyl, methylene, ethylidiene, phenyl or benzyl; R5 can be a methylene, ethylene, propylene or phenylene group. The ammonium and/or phosphonium cation is preferably selected from the group formed by N-butylpyridinium, N-ethylpyridinium, 3-ethyl-1-methylimidazolium, 3-butyl-1-methylimidazolium, diethylpyrazolium, pyridinium, trimethylphenyl ammonium and tetrabutyl-phosphonium. Examples of salts which can be used in the invention which can be cited are N-butylpyridnium hexafluorophosphate, N-ethylpyridinium tetrafluoroborate, tetrabutylphosphonium tetrafluoroborate, 3-butyl-1-methylimidazolium tetrafluoroborate, 3-butyl-1-methylimidazolium hexafluoroantimonate, 3-butyl-1-methylimidazolium hexafluorophosphate, 3-butyl-1-methylimidazolium trifluoromethylsulfonate, pyridinium fluorosulfonate and trimethylphenylammonium hexafluorophosphate. These salts can be used alone or as a mixture.
The catalytic composition is obtained by mixing the liquid salt with the cobalt and/or rhodium compound and the nitrogen-containing ligand in any known manner. It is also possible to first dissolve the transition metal compound (cobalt and/or rhodium) and/or the ligand in the organic solvent.
The complex between the cobalt and/or rhodium precursor and the nitrogen-containing ligand can be prepared prior to the reaction by mixing the cobalt and/or rhodium precursor with the ligand in a suitable solvent, for example an organic solvent or the non-aqueous ionic solvent which will then by used in the catalytic reaction. The complex can also be prepared in situ by mixing the cobalt and/or rhodium precursor and the nitrogen-containing ligand directly in the hydroformylation reactor.
In general, the catalytic composition can contain a miscible or partially miscible organic solvent such as an aromatic hydrocarbon, and/or a non-miscible aliphatic hydrocarbon which enables better phase separation. Preferably, the catalytic composition contains no water.
The concentration of cobalt and/or rhodium complex in the ionic liquid xe2x80x9cmolten saltxe2x80x9d is not critical. It is advantageously in the range 0.1 moles per liter of xe2x80x9cmolten saltxe2x80x9d to 5 moles per liter, preferably in the range 1 mole to 1 mole per liter, still more preferably in the range 100 to 500 moles per liter. The mole ratio between the nitrogen-containing ligand and the cobalt and/or rhodium compound is in the range 0.1 to 100, preferably in the range 1 to 20.
The components in the composition of the invention can be mixed in any order at a temperature in the range xe2x88x9220xc2x0 C. to 200xc2x0 C., preferably in the range 0xc2x0 C. to 140xc2x0 C., and advantageously in the range 20xc2x0 C. to 90xc2x0 C.
Olefinically unsaturated compounds which can be hydroformylated are selected from the group formed by monoolefins, diolefins, in particular conjugated diolefins and olefinic compounds comprising one or more heteroatoms, in particular unsaturated compounds such as compounds with a ketone function or a carboxylic acid function. Examples which can be cited are hydroformylation of pentenes to hexanal and methylpentanal, hexenes to isoheptanals, isooctenes to isononanals. These olefinic compounds can be used pure or diluted with saturated or unsaturated hydrocarbons.
The ratio of the partial pressures of hydrogen to carbon monoxide used in the reaction medium for hydroformylation can be 10:1 to 1:10, preferably in a ratio of 1:1, but any other ratio can be used depending on the implementation of the process.
The temperature at which hydroformylation is carried out is in the range 30xc2x0 C. to 200xc2x0 C.; advantageously the temperature is less than 150xc2x0 C., preferably in the range 50xc2x0 C. to less than 150xc2x0 C. The pressure can be in the range 1 MPa to 20 MPa, preferably in the range 2 MPa to 15 MPa.
Catalytic hydroformylation of the unsaturated compounds can be carried out in a closed system, in a semi-open system or continuously with one or more reaction stages. At the reactor outlet, the organic phase containing the reaction products is advantageously separated by simple decantation of the ionic solvent phase containing the xe2x80x9cmolten saltxe2x80x9d and the major portion of the catalyst. This ionic solvent phase, which contains at least a portion of the catalyst, is at least partially returned to the reactor, the other portion optionally being treated to eliminate the catalyst residues.
The entire disclosure of all applications, patents and publications, cited above and below, and of corresponding French application 99/15573, filed Dec. 8, 1999, are hereby incorporated by reference.
The following examples illustrate examples of using the catalyst of the invention without limiting its scope.